Radio-controlled scale model vehicle racing is a popular hobby sanctioned by Radio-Operated Auto Racing, Inc., among other rule making organizations. Competition events often feature model cars, model aircraft, and model boats. Racing heats are generally staged on a closed-circuit race course and require each competing model vehicle to complete as many laps as possible within a specified time period, with the model completing the largest number of laps being declared the winner. Some racing events are conducted over an unimproved off-road outdoor area where the model vehicle must be steered carefully to avoid collision with obstacles. When a collision occurs, it may be necessary to drive the model car in reverse to clear the obstacle before the race can be continued.
Each scale model vehicle is controlled in terms of steering, throttle and forward/reverse travel by low-power, digitally encoded radio-frequency command signals at a dedicated frequency generated by a hand-held remote control transmitter, for example. Each model is equipped with an onboard radio receiver that is tuned to the same frequency as the transmitter. The radio receiver provides control signals and power to servos that are actuated to cause the model to turn, increase speed, slow down, and reverse direction as commanded by the operator.
There are two main categories of radio-controlled scale model vehicles, battery-powered and fuel-powered. The prime mover in a battery-powered vehicle is an electric motor, while the prime mover in a fuel-powered vehicle is an internal combustion engine. Because fuel-powered vehicles typically do not have an onboard electrical generating system, a small battery is usually included to provide electrical power for operating onboard radio system components. The onboard radio system components typically include a receiver and servo motors. Conventional battery-powered vehicles typically achieve reversal of the prime mover (an electric motor) by reversing the polarity of the applied voltage. Most internal combustion engines are not reversible, and thus reversing the engine direction is typically not an option for providing reverse motion of the vehicle.
One conventional radio-controlled scale model vehicle is equipped with an onboard battery and a DC electric motor for cranking the internal combustion engine during starting, and also for providing motive power during reverse travel operation. The internal combustion engine in this case is not reversible, but provides operating power for the model vehicle during forward travel operation. The forward gear is disengaged and the engine is brought to idle under servo-control to permit transfer to the DC electric motor through a power transfer linkage and a reverse gear so that the model vehicle can be propelled by electrical power in the reverse direction using the starter motor.
It will be appreciated that the sequential shifting operation, which requires transition to idle speed, disengagement of the fuel engine and engagement of the electric drive motor, imposes an undesirable time delay before the vehicle motion can be completely reversed. Additionally, if the electric drive motor is engaged in a reverse direction while the vehicle is being operated at a high rate of speed, the gearing, and/or power transfer linkage may be damaged. Accordingly, there is a need for a simple, rapid, and reliable means for selectively reversing the forward driving torque produced by a prime mover, for example an internal combustion engine or inertial flywheel motor that is not reversible, into reverse driving torque, thus eliminating the need for an onboard battery and electric drive motor for reverse travel. Additionally, a shiftable transmission is needed for use in combination with a radio-controlled scale model vehicle in which shifting from forward to reverse is performed without damaging the transmission gear train or linkage.
A shift lockout means is desired for a transmission having a capability of shifting between forward and reverse to prevent damage to the drive train components, and to prevent loss of control and crashing that often occur if a shift is executed while the transmission is operating at high RPM.
Traxxas Corporation has provided a mechanical means of limiting the shifting from forward to reverse, which is disclosed in U.S. Pat. No. 6,367,345 (“the '345 patent”). An embodiment of this mechanical shift lockout system disclosed in the '345 patent includes an arrangement of mechanical components within the transmission designed to prevent shifting between forward and reverse directions when the vehicle's transmission is rotating above a certain rotational speed (e.g., revolutions per minute—RPM). The mechanical shift lock system includes a one-way centrifugal lock-out clutch including springs to counter centrifugal forces caused by the rotation of a drive shaft within the transmission. However, it would be desirable to provide a more simplified system (mechanically) that may provide forward/reverse shifting performance comparable to or better than that of the mechanical shift lockout system disclosed in the '345 patent, while still using the primary motive force (i.e., the internal combustion engine used for forward motion) for providing reverse motion.